fyi rounding modes that work with FloatNN

[JeffreySarnoff]

setrounding(Float64, MODE) works for these RoundingModes
RoundNearest, RoundUp, RoundDown, RoundToZero

setrounding(BigFloat, MODE) works for these RoundingModes
RoundNearest, RoundUp, RoundDown, RoundToZero, RoundFromZero

to emulate RoundFromZero on FloatNNs (similarly with (fn, x, y) and (fn, x, y, z)

function roundfromzero(fn, x::T) where {T}
   @nospecialize fn, x
    initialmode = rounding(T)
    roundingmode = signbit(x) ? RoundUp : RoundDown
    setrounding( T, roundingmode)
    result = fn(x)
    setrounding(T, initialmode)
    return result
end

If its not in the docs .. it should be (I have not looked).